In the professors lab, in the two-shot Jimmy has his arm around Nancy. When they cut to the shot of the three of them, Jimmy has his arm by his side and then reaches up to put it around Nancy. Moments later, in the next shot, Jimmy has his arm by his side again.
The photo that Jimmy took of Professor Quinn, Nancy and Clark shows that the three weren't looking at the camera when it was taken, but somewhere to the right.
When Jimmy sets off the sprinkler and the fire alarm in the secret room, the professor and Nancy both have to boost him up to the ceiling so that he can reach the sprinkler. Yet, when Superman breaks through from the room above to rescue the three, all of them are able to reach their hands up to the hole created by Superman, allowing him to merely reach down to the hole, grab their hands, and lift each one to safety. The first two might conceivably have been boosted up, but not the third.
When Kent pounds the postage stamp and it explodes no one finds it unusual that he wasn't injured at all, even though it was powerful enough to throw the other people across the room, and the best proof that he is Superman.